Lesson 1 - Chemical Reactions and Equations (Exercise-10)

 Solution 1

(i)            The substance 'X' is Calcium Oxide (lime). Its Chemical formula is CaO.

(ii)           Calcium Oxide reacts vigorously with water to form Calcium Hydroxide (slaked lime).   

Insight Concept: The answer is white washing. Think of the substance used for white washing and answer accordingly.

Solution 2

Water (H2O) contains two parts of hydrogen and one part of oxygen. Therefore, the amount of hydrogen and oxygen produced during electrolysis of water is in a 2:1 ratio. During electrolysis, since hydrogen goes to one test tube and oxygen gas goes to another hence, the amount of gas collected in one of the test tubes is double the amount collected in the other.  The gas collected in double the amount is hydrogen and the other gas is oxygen.

Insight Concept: The key to this answer is the electrical decomposition reaction of water.

Lesson 1 - Chemical Reactions and Equations (Exercise-13)

 Solution 1

When an iron nail is placed in a copper sulphate solution, iron displaces copper from the blue colored copper sulphate solution forming light green colored ferrous sulphate solution and copper metal.

Insight Concept: A displacement reaction takes place when iron nails are dipped in copper sulphate solution. Recall that iron is a more reactive metal than copper.

Solution 2

A double displacement reaction between the reactants lead nitrate and potassium iodide gives new substances: a yellow ppt. of lead iodide and potassium nitrate.

 In this reaction, lead nitrate and potassium iodide exchange ions to form two new compounds lead iodide and potassium nitrate. Hence, it is a double displacement reaction.

Insight Concept: Recall that two different atoms or groups of atoms (ions) are exchanged in double displacement reactions.

Solution 3

(i)     Sodium (Na) is oxidized to sodium oxide as it gains oxygen and oxygen (O2) gets reduced.

(ii)   Copper oxide (CuO) is reduced to copper (Cu) while hydrogen (H2) gets oxidized to water (H2O).

Insight Concept: Recall that oxidation reaction is gain of Oxygen and reduction reaction is release of Oxygen.

Lesson 1 - Chemical Reactions and Equations (Exercise-15)

Solution 1

(a) Hydrogen gas and Iron Chloride are produced.  

Insight Concept: you know that metals react with hydrochloric acid to form respective metal chlorides and liberate hydrogen gas.

Solution 2

A chemical equation is balanced when the numbers of atoms of each type involved in a chemical reaction are same on both the reactant and product sides of the equation.

The chemical equations must always be balanced to satisfy the law of conservation of mass which states that "Mass can neither be created nor destroyed in a chemical reaction." This means that the total mass of the elements present in the products of a chemical reaction has to be equal to the total mass of the elements present in the reactants. Hence, the number of atoms of each element in the products must be equal to the number of atoms of these elements in the reactants. 

Insight Concept: Recall that a chemical equation should be balanced to follow the Law of conservation of mass.

 Solution 3

(a) 3H2 + N2 ---> 2NH3

(b) 2H2S + 3O2 --->  2H2O + 2SO2

(c) 3BaCl2 + Al2(SO4)3 --->  2AlCl3 + 3BaSO4

(d) 2K + 2H2O --->  2KOH + H2

Insight Concept: Convert the word equation into skeletal equation and then balance the different atoms on both sides of the equation.

Solution 4

(a) 2HNO3 + Ca(OH)2 ---> Ca(NO3)2 + 2H2O

(b) 2NaOH + H2SO4 ---> Na2SO4 + 2H2O

(c) NaCl + AgNO3  ---> AgCl + NaNO3

(d) BaCl2 + H2SO4 ---> BaSO4 + 2HCl

Insight Concept: Write all the different types of atoms on both the reactant and product side. Balance them one by one.

Solution 5

(a) Ca(OH)2 + CO2  ---> CaCO3 + H2O

(b) Zn + 2AgNO3  ---> Zn(NO3)2 + 2Ag

(c) 2Al + 3CuCl2  ---> 2AlCl3 + 3Cu

(d) BaCl2 + K2SO4 --->  BaSO4 + 2KCl

Insight Concept: Convert the word equation into skeletal equation and then balance the different atoms on both sides of the equation.

Solution 6

(a)   2KBr (aq) + Bal2  ---> 2Kl (aq) + BaBr2 (s), Double displacement reaction and precipitation reaction

(b)   ZnCO3 (s) --->  ZnO (s) + CO2 (g), Decomposition reaction

 (c)  H2 (g) + Cl2 (g)  ---> 2HCl(g), Combination reaction

(d)   Mg(s) + 2HCl(aq)  ---> MgCl2 (s) + H2 (g), Displacement reaction

Insight Concept: Convert the word equation into skeletal equation and then balance the different atoms on both sides of the equation. Write the states of all the Reactants and products in brackets. Then identify the type of reaction by recalling all the type of chemical reactions and match with the reactions one by one. A combination reaction involves one product and decomposition reaction involves one reactant. For identifying whether it is displacement reaction or not, see whether two displacements are taking place or one. If one it is displacement reaction and if two displacements are taking place, it is double displacement reaction.

 Solution 7

Reactions in which heat is released along with the formation of products are called exothermic reactions. Example of exothermic reaction:

Burning of natural gas: CH4(g) + 2O2 (g)  ---> CO2 (g) + 2H2O (g) + Heat

Reactions in which energy is absorbed are known as endothermic reactions. Example of endothermic reaction:

2AgBr(s) ----sunlight------->  2Ag(s) + Br2(g)

Insight Concept: Can you remember that in one reaction, energy is released and in the other, energy is absorbed. Exo means out of or outside so exothermic means that energy is released. Endo means inside so endothermic means that energy is absorbed.

Solution 8

Food that we eat includes carbohydrates, proteins, vitamins etc. During digestion, carbohydrates are broken down into simpler substances called glucose. Glucose combines with oxygen in the cells of our body to form carbon dioxide and water along with energy. This reaction is called respiration. Since energy is released during this process, respiration is an exothermic reaction.                                   

Insight Concept:  You should know what exothermic reactions are and then relate it to respiration.

Solution 9

In a decomposition reaction, a single substance decomposes to give two or more substances. Whereas in a combination reaction two or more substances combine to form a new single substance. And hence, decomposition reactions are opposite of combination reactions.

Decomposition reaction: AB + Energy -->  A + B

Example:

CaCO3(s) -->  CaO(s) + CO2(g)

Combination reaction: A + B -->  AB + Energy

Example: Burning of coal:   C(s) + O2(g) -->  CO2(g)

Insight Concept: Please go through what combination and decomposition reactions are and then reason whether they are opposite of each other or not.